1. Field of the Invention
The present invention relates to a bioreactor carrier, a process for producing the carrier and a method for using the same. More particularly, it pertains to a bioreactor carrier which is imparted with water swelling properties, a specific gravity controlled within a specific range, and high physical strength; enables microbial reactions and enzymatic reactions to be effectively performed; and moreover is readily producible, to a process for producing the carrier in high efficiency, and to a method for effectively carrying out denitrifying treatment for organic waste water with microbes by the use of the above-stated carrier.
2. Description of the Related Arts
The carriers to be employed in bioreactors can be broadly classified into porous carriers and gel carriers. Examples of the porous carriers include those made of polyurethane, cellulose, polypropylene, polyvinyl formal, ceramic etc., respectively. Because of their being porous, the carriers have a large surface area and in the majority of cases, are employed in a state of binding immobilizing animal cells, plant cells, microbes and/or protozoans onto the porous surfaces thereof.
However, the above-mentioned porous carriers suffer from various disadvantages and drawbacks as described hereunder. Polyurethane and polypropylene porous bodies, because of their being hydrophobic, have inferior fluidity in water and in addition, make it difficult for animal cells, plant cells, microbes and/or protozoan to be bonded thereonto. Cellulose porous bodies are subject to attack by microbe, whereby their service life is unfavorably shortened. With regard to polyvinyl formal porous bodies, an industrial process for producing the same is not yet established. Ceramic porous bodies can not be fluidized in water due to their high specific gravity, thereby inevitably restricting the usage.
On the other hand, there are known as gel carriers, those made of polyacrylamide, polyethylene glycol, polyvinyl alcohol and alginic acid, thermoplastic water absorbing bodies, etc., respectively {refer to Japanese Patent Application Laid-Open No. 136980/1998 (Heisei-10)}. It is a general practice to use these gel carriers by entrapping immobilizing animal cells, plant cells, microbes and/or protozoans at the inside of the gel, and alternatively it is possible to use the above-mentioned carriers by binding immobilizing animal cells, plant cells, microbes and/or protozoans onto the gel surfaces.
The aforesaid gel carriers, which highly contain water, generally have high affinity for living matters and at the same time, impart favorable habitat to animal cells, plant cells, microbes and/or protozoans. Nevertheless, the physical strength is not necessarily sufficient in such carriers as those made of polyacrylamide, polyethylene glycol, polyvinyl alcohol and alginic acid, which bring about a fear of wear and collapse in the course of service in a reaction tank. In addition, the gel carriers just mentioned, when once molded into a definite shape, can not be changed to an other shape by remelting. Thus, such carriers are generally cut into a required shape in the majority of cases. In fact, the gel carriers suffer from serious disadvantages in that the step of cutting the water-containing and swollen gel into several millimeter sized regular hexahedron requires tremendous labor and period of time with the result that the production thereof becomes extremely intricate and troublesome, thus necessitating markedly long time and high cost in production.
As opposed to the foregoing, thermoplastic water absorbing gel carriers that are typified by thermoplastic water absorbing polyurethane gel carriers are well suited for use as bioreactor carriers owing to such advantages as high physical strength, capability of industrial mass production, capability of adsorbing animal cells, plant cells, microbes and/or protozoans due to their hydrophilicity without deteriorating the physiological activity thereof, favorable resistance to attack by microbes and the like.
In this connection, utmost importance is attached to the specific gravity of the bioreactor carriers. For instance, the specific gravity thereof, when being close to that of water on attaining steady state of adhesion, bonding and immobilization of microbes in a reactor, gives rise to such a problem, in the case of fluidizing the liquid to be treated in a reactor for the purpose of reaction, that the microbes are apt to move upwards and difficult to be present in the lower portion, thus causing failure to assure uniform fluidity and deteriorating the efficiency of microbe reaction.
In such circumstances, an object of the present invention is to provide a bioreactor carrier which is imparted with water swelling properties, a specific gravity controlled within a specific range, and high physical strength; enables microbial reactions and enzymatic reactions to be effectively performed; and moreover is readily producible, to a process for producing the carrier, and to a method for using the same.
Other objects of the present invention will be obvious from the text of this specification hereinafter disclosed.
In order to achieve the above-mentioned objects, research and investigation were intensively and extensively accumulated by the present inventors. As a result, it has been found that a bioreactor carrier which conforms to its purpose of application is obtainable by adding a specific inorganic filler to a water swellable thermoplastic resin such as water swellable thermoplastic polyurethane resin at the time of producing the resin and/or molding the same; controlling the specific gravity within a specific range; and thereafter molding the mixed resin into a desirable form by means of an extruder, and at the same time that organic waste water can effectively be subjected to denitrification treatment by using the molding thus obtained as a carrier for immobilizing microbes in nitrifying and denitrifying nitrogenous components in the organic waste water. The present invention has been accomplished on the basis of such findings and information.
That is to say, the present invention provides:
(1) a bioreactor carrier comprising a (A) water swellable thermoplastic resin and (B) at least one inorganic filler which is added thereto at the time of producing and/or molding said resin and which is selected from the group consisting of barium sulfate, silica, kaolin, quarts sand, diatomaceous earth, barite, talc, alumina, titanium dioxide and iron oxides, with the proviso that any of barium sulfate, kaolin, diatomaceous earth and talc, when being added thereto at the time of molding, is subjected to dehydrating treatment in advance, characterized in that the specific gravity of said carrier on swelling in water is controlled within the range of 1.02 to 1.35;
(2) a process for producing a bioreactor carrier the specific gravity of which on swelling in water is controlled within the range of 1.02 to 1.35, comprising the steps of blending at least one inorganic filler selected from the group consisting of barium sulfate, kaolin, diatomaceous earth, talc, each of which has been subjected to dehydrating treatment, silica, quarts sand, barite, alumina, titanium dioxide and iron oxides with a water swellable thermoplastic resin; thereafter heat melting the resultant blend; extruding the molten blend through an extruder into the form of strand; and continuously cutting the strand;
(3) a process for producing a bioreactor carrier the specific gravity of which on swelling in water is controlled within the range of 1.02 to 1.35, comprising the steps of blending at least one inorganic filler selected from the group consisting of barium sulfate, silica, kaolin, quarts sand, diatomaceous earth, barite, talc, alumina, titanium dioxide and iron oxides at the time of producing a water swellable thermoplastic resin from reactants of said resin; thereafter heat melting the resultant blend as such or after further blending of said at least one inorganic filler with the proviso that any of barium sulfate, kaolin, diatomaceous earth and talc, when being added thereto, is subjected to dehydrating treatment in advance; extruding the molten blend through an extruder into the form of strand, and continuously cutting the strand; and
(4) a process for denitrifying treatment of organic waste water which comprises nitrifying and denitrifying nitrogen components in the organic waste water with microbes by the use of the bioreactor carrier as set forth in the preceding item (1).